Radio frequency tuners having variable tracking and coupling means



Sept. 5, 1961 F, G. MASON ET Ax.

RADIO FREQUENCY IUNERS HAVING VARIABLE TRACKING AND COURLING MEANS 2Sheets-Sheet 1 Filed Jan. 14, 1959 IMJ N? Nmmml Sept. 5, 1961 F. G.MASON ET AL 2,999,156

RADIO FREQUENCY TUNERS HAVING VARIABLE TRACKING AND COUPLING MEANS FiledJan. 14, 1959 2 Sheets-Sheet 2 INVENTORS United States Patent C2,999,156 RADIO FREQUENCY TUNE-RS HAVING VARIABLE TRACKING AND COUPLINGMEANS Francis G. Mason, Weston, and Harold T. Lyman, Milford, Conn.,assignors to Aladdin Industries, Incorporated, Nashville, Tenn., acorporation of Illinois Filed Jan. 14, 1959, Ser. No. 786,7 17 6 Claims.(Cl. Z50-40) This invention relates to radio frequency tuners and isparticularly applicable to tuners adapted to cover an extremely widefrequency range.

One object of the present invention is to provide a new and improvedtuner of the foregoing character which has a pair of tuned circuits ortuning devices, together with means for adjusting the coupling betweenthe circuits to the desired value throughout the tuning range, and alsomeans for tracking the tuned circuits to the same tuning curvethroughout the frequency range.

A further object is to provide a new and improved tuner of the foregoingcharacter having variable coupling and tracking devices which areoperated by` adjustable cams.

Another object is to provide such a new and improved tuner in which eachof the cams has a large number of individually bendable tabs foradjusting the coupling and tracking at a large number of pointsthroughout the tuning range.

A further object is to provide such a new and improved tuner in whichthe tuning devices are tuned by means of members movable simultaneouslyalong predetermined substantially parallel paths, and in which the camsextend generally parallel to such paths, for cooperation with camfollowers or riders which are mounted on the movable tuning members.

Still another object is to provide new and improved tuners of theforegoing character which afford precise adjustment of the tracking landcoupling, yet are serviceable, reasonably easy to manufacture, and lowin cost.

Further objects and advantages of the invention will appear from thefollowing description, taken with the accompanying drawings, in which:

FIG. l is a plan view, partly in longitudinal section, of a tuner to bedescribed as an illustrative embodiment of the present invention.

FIGS. 2 and 3 are elevational sectional views, taken generally alonglines 2 2 and 3 3 in FIG. l.

FIG. 4 is a fragmentary view similar to the central portion of FIG. l,but showing certain modifications.

FIG. 5 lis a fragmentary enlarged plan View showing another modiiiedconstruction.

FIG. 6 is a cross sectional view, taken generally along the line 6 6 inFIG. 5.

As already indicated, FIGS. l-3 illustrate a radio frequency tuner 10adapted to cover an extremely Wide frequency range. The illustratedtuner comprises a pair of tuned circuits or tuning devices l12a and 12bwhich are adapted to be tuned to substantially the same operatingfrequency. The tuning devices 12a and 12b are provided with tuningmembers 14a and 1'4b which are movable along predetermined paths to varythe operating trequency. In this case, the members 14a and 14h aremovable along straight line paths which are substantially parallel.

Coupling between the tuning devices 12a and 12b is provided by avariable coupling device 16. As will be described in detail shortly, thetuner 10 is provided with means for adjusting the coupling device 16 asthe tuning members 14a and 1'4b are moved along their paths, so as toprovide the desired `amount of coupling throughout the tuning range ofthe tuner 10. A variable tracking device ice 18 is providedito effectslight variations in the tuning of one of the tuning devices 12a and12b, so that the operating frequencies of the tuning devices will betracked to the same tuning curve as the tuning members 14a and 14b aremoved along their paths to cover the frequency range of the tuner.

The invention is lapplicable to a Wide variety of tuners. However, byway of example, each of the illustrated tuning devices 12a is providedwith an elongated generally helical inductance coil 20, which iscircular in cross section, as shown in FIG. 3. The axis of each coil 2i)is straight. In this case, the tuning members 14a and 1417 take thelform of conductive cylindrical electrodes or.

tween, so that the sleeve will be capacitively coupled tov theunderlying portion of the coil. Preferably, the dielectric element takesthe form of a coating 22 on the coil 20, asV shown to best advantage inFIG. 6. In this regard, the rtuner of FIG. 6 is the same as that ofFIGS.V

In this case, each coil 20 extends along the axis of a correspondingconductive cylinder or tube 24, which shields the coil and providescoupling to the tuning sleeve I4. The tubes 24 are shown as beingconnected together by means of a grounded conductor 26, although variousother connections may be made to the tubes. Each of the tuning sleeves14a and 14b is closely received within the corresponding tube 24, forsliding movement therealong. While each sleeve 14 may be conductivelyengaged with the corresponding tube 24, it is preferred to provideinsulation therebetween, so that the sleeve will be capacitively coupledto the tube. The insulation may advantageously take the form of adielectric coating 28 applied to each sleeve, as shown to advantage inFIG. 3. The provision of the coatings 22 and 23 on the coil 20 and thesleeves 14a and 14h eliminates any electrical noises that might resultvif the sleeves were in sliding electrical contact with the coils 20 andthe tubes 24.

The illustrated tuning sleeves 14a yand 14b are connected together forsimultaneous movement by an operating member or block 30. The sleeves14a and 1412 are securely connected to the block `3l) by means of shortbars 32 or the like which extend through longitudinal slots 34 [formedin the tubes 24. The block 30 may be moved along a linear path byvarious means, such as the illustrated lead screw 36, which is threadedthrough the block. The lead screw 36 may be rotated by any suitablemeans (not shown).

As shown, the left-hand end of each coil 20 is formed with a cylindricalterminal portion 38 which may form one circuit terminal of thecorresponding tuned circuit 12. The tube 24 may provide a second circuitterminal. It will be recalled that the tube 24 is capacitively coupledto the correspondingsleeve 1'4, and that the sleeve is capacitivelycoupled to ,the underlying portion of the coil 20. Thus, only theportion of the coil 20 to the left of the sleeve 14 is' in the tunedcircuit between the terminal portion 38 and the tube 24. Thus, theeffective inductance of each of the tuning devices 12a and 12b isincreased as the corresponding sleeve 14 ismoved to the right. Thisinductance is resonated by the stray or distributed capacitances 69between the coil 20 and the tube 24. These stray capacitances 39 areeffectively in series with the capacitances between the sleeve and thetube Z4, and between the coil 20 and the sleeve .14. Any externalcapacitance that may be introduced between the terminal portion 38 andthe tube 24 also contributes tothe resonating effect. It will beunderstood that the resonant frequency er each tunasleviss increases asthe sleeve is ,moved t9 the left, land decreases with movement of thesleeve to the right.

In addition to changing the inductance of the coil 20, the movement ofeach sleeve 14 varies the efiective stray capacitance 39 between thecoil and thetube 24. The stray capacitance increases progressively asthe sleeve is moved to the right. It will be recalled that such movementof the sleeve also increases the effective inductance of the coil 20.Thus, the increasing stray capacitance extends the range of the tuner.This is' a matter of considerable advantage.

As shown, an external capacitor 40 may be connected between eachterminal portion 38 and ground. Preferably, the capacitors 40 arevariable. I t will be recognized that the capacitors 40 are in parallelwith the stray capacitances 39. In many cases, the capacitors 4,0 willnot be needed to resonate the coils 20 in the desired frequency range.In that case, the capacitors may be omitted, and the terminals 38 may beleft lioating. In some cases, the terminal 38 of the second tuningdevice 12b may be connected to the grid of `a tube, or to some othercircuit element, by an output lead 4.1.

Various arrangements may be employed to supply input energy to the tuner10, and to take output energy thercfrom. In this case, the input issupplied by means of an input coil 42, while the output is taken by anoutput coil 44. Each coil is preferably made of a few turns of heavywire so as to be self-supporting. The coil 42 is disposed around thecoil 2i), adjacent the left-hand end of the sleeve 14a. One end of thecoil 42 is connected, both electrically `and mechanically, to the block30 and thence to the sleeve 14a. The other end of the coil takes theform of a terminal portion 46 which extends out of the tube 24 through aslot 48 therein. Similarly, one end of the coil 44 is connected to thesleeve l4b, while the other end of the coil takes the form of a terminalportion S which extends outwardly through a slot 51 in the correspondingtube 24. Thus', the input and output coils 42 and 44 are movable withthe sleeves 14a and 14b. Suitable flexible connections may be made tothe terminal portions 46 and 50, as will be described in greater detailshortly.

Certain modifications or elaborations of the tuner are shown in FIG. 4.As shown, the sleeves 14a and 14b of FIG. 4 are supplemented by rings orauxiliary sleeves' 52a and 52b which are secured to the operating block30 by means of members 54. The rings 52a and 52h are disposed around thecoils to the right of the sleeves 14a and 14b. It will be apparent that`the rings 52a and 52h are movable along the coils 20, with the sleeves14a and 14b. While the rings 52a and 52b might be conductively engagedwith the coils 20 and the tubesI 24, it is preferred to insulate therings so that they will be capacitively coupled to the coils and thetubes. The coating 22 on each coil 20 provides insulation between thecoil and the corresponding ring 52. A dielectric coating 56 may beapplied to each ring S2 to insulate the ring from the corresponding tube24.

The rings 52a and 52h perform the function of suppressing spuriousresonances in the portions of the coils 20 to the right of the sleeves14a and 14]). Were it not for the rings 52a and 521:, these portionsofthe coils would' be floating and would tend to be self-resonant atunwanted frequencies. The provision of the rings 52a and 52b has -apronounced damping effect on such self-resonances, so that they are nolonger troublesome. The spacing between each ring 52 and thecorresponding sleeves 14 results in a high degree of damping throughoutthe tuning range.

As shown in FIG. 4, the input lead 46 is connected to the centralconductor 56 of a flexible coaxial input cable 58. The outer conductor60 of the cable 58 is connected to a housing or shield 62 which extendsaround the tubes 24 and is secured to the operating block 30 so as totravel with the sleeves 14a and 14b.

The output lead 50 may be connected to a suitable detector and amplifiercircuit 64 mounted within the shield 62. A exible coaxial cable 66 isconnected to the output of the amplifier 64.

In this case, the threaded operating block 30 is provided with contactsprings 68 which wipe against the tubes 24 to ground the block. Similargrounding springs 70 are provided on the shield 62.

The tuned circuits 12a and 12b may be tracked rather closely to the sametuning curve, by the simple expedient of making all components of thetuned circuits as nearly identical as possible. However, it is virtuallyimpossible to make the tuning circuits totally identical, with theresult that there will tend to be an appreciable tracking error. Asalready indicated, the illustrated tuner 1t) is provided with anadjustable tracking device 18 to compensate for any tracking error, soas to secure tracking which is sulficiently accurate for all practicalpurposes.

The adjustable tracking device 18 comprises an element 70 which ismovably mounted on one of the tuning members 14a and 14b, in this casethe member 14a. Movement of the element 70 is effective to vary thetuning of the circuit .12a to a small extent, which, however, issufficient to compensate for -any tracking error. The tracking device 18is' -arranged so that the position of the tracking member 70 may beadjusted at a large number of points throughout the range of movement ofthe tuning members 14a and 14b. In this way, precise tracking may beachieved throughout the tuning range.

The illustrated tracking member 70 takes the form of a conductive ringwhich is positioned around the coil 20 to the left of the sleeve 14a.The ring 70 is movable axially with respect to the sleeve 14a. Suchmovement of the ring 7G changes the effective inductance of the coil 20to a small extent. Thus, the inductance of the coil 20 is decreased bymovement of the ring 70 to the left, and increased by movement of thering to the right. The ring 70 is made thin, and is spaced from the coil20 and the tube 24, so that lthe tuning of the coil Z0 will be changedonly to a smal-1 extent when the ring is moved.

As shown, the tracking ring 70 is secured to guide rods 72 which areslidable in bores 74 formed in the sleeve 14a. The bores 74 extendparallel to the axis of the sleeve 14a.

The movement of the tracking ring 70 is controlled by a cam 76 whichtakes the form of a plate extending generally parallel to the path ofmovement of the sleeve 14a. The cam plate 76 is engaged by the camfollower 78 Which is formed on the end of an arm 80. lt will be seenthat the arm 80 forms one portion of an L-shaped lever 82 which isswingable about a pivot 84. The lever 82 has a second arm 86 which isarranged to move the ring 70. Thus, the arm 86 extends generally atright angles to the direction of the guide rods 72. A longitudinal slot88 is formed in the end of the arm 88, for slidably receiving a pin 90.As shown to advantage in FIGS. l and 3, the pin 9i] extends upwardlyfrom a guide rod 92 which is slidable in a bore 94 formed in the block30. One of the guide rods 72 is connected to the rod 92 by a member 96.Thus, any swinging movement of the arm 86 is translated intoreciprocating movement of the member 70.

The pivot 84 is mounted on a member 98 which is secured to the block 30.A spring is stretched between the member 98 and the arm 86, so as tobias the lever 82 clockwise, and thereby hold the follower 78 againstthe cam 76.

The cam plate 76 may be bent locally so as to adjust the position of thetracking ring 7) at various points in the movement of the tuning sleeve14a. To provide for easy, accurate adjustment, the cam plate 76 isformed with a large number of slots 104, spaced along the length of thecam and preferably extending transversely to the direction of movementof the tuning sleeve 14a. The slots 104 divide the cam 76 into a largenumber of indvidually bendable fingers or tabs 106. At any point inthemovemeri't of the sleeves 14a, the follower 78 will be engaging oneof the tabs 186. Precise tracking may be obtained by bending thisparticular tab 106 so as to move the follower 78, and thereby shift thetracking ring 70. The tab is bent to such a position that the `tunedcircuit 12a will be adjusted to the same frequency as the tuned circuit12b.

As already indicated, the variable coupling device 16 is provided sothat the coupling between ithe tuned circuits 12a and 12b may beadjusted at various points throughout the tuning range of the tuner 1i).Any suitable type of coupling may be provided between the itunedcircuits 12a and 12b. Thus, for example, either inductive coupling orcapacitive coupling may be utilized. As shown, the variable couplingdevice 16 provides capacitive coupling, which is variable so that thedesired coupling may be obtained throughout the tuning range. Of course,the amount of coupling affects the Width of the band passed by thetuner. The coupling may be adjusted to maintain the band Widthsubstantially constant, or to provide desired changes in the band widthfrom one portion of the band to another.

In the illustrated arrangement of the coupling device 16, the capacitivecoupling is provided by a pair of electrodes 110 which are slidablymovable along the respective coils 20. As shown, each electrode 110takes the form of a discontinuous ring, having a longitudinal slot 112formed therein. The formation of the slots 112i prevents the rings 116from acting as short circuited turns. The electrodes 11i) are connectedtogether, both electrically and mechanically, by a bar 114, whichextends through the slots 34 in the tubes 24. Thus, the interconnectedelectrodes 118 establish capacitive coupling between the coils 20. Asshown, each electrode 110 is received part way over the left-hand end ofthe corresponding coil. The degree of coupling may be increased anddecreased by moving the electrodes 118 to the right and to the left,respectively, as indicated by the broken line positions of theelectrodes in FIG. l. The extent to which the left-hand ends of thecoils 20 are received Within the electrodes 11@ increases as theelectrodes are moved to the right, and decreases with movement of theelectrodes to the left.

The variable coupling mechanism 1,6 is arranged so that the position ofthe electrodes may be changed as the tuning sleeves 14a and 1411 aremoved along the coils 20. In the illustrated construction, thisoperation is achieved by providing an adjustable cam 118' which isadapted to move the electrodes 110. As shown, the cam 118 takes the formof a plate extending along the paths of the tuning sleeves 14a and 14h.The cam plate 11S is secured to a shaft 126 which is rotatable about anaxis parallel to the paths of the sleeves 14a and 1411. By means of anL-shaped lever 122, the shaft 120 is connected to the bar 1141i, andthence to the electrodes 110. It will be seen that the lever 122 isswingable about a vertical pivot 124. The `lever 122 has a relativelyshort arm 126 which is connected to the shaft 120, and a relatively longarm 128, connected to the bar 114. A slot 130 is formed in the end ofthe arm 126 to receive a pin 132 extending radially from the shaft 128.By means of this pin-and-slot connection, any rotation of the shaft 120causes swinging movement of 4the lever 122.

Similarly, a slot 134 is formed in the end of the arm 128, to receive apin 136 extending upwardly from an insulating block 138 mounted on thebar 114. This pinand-slot connection translates any swinging movementofthe lever -122 into reciprocating movement of the bai' 114.

The position of the cam 118 is controlled by a rider 142 which engagesthe cam and is movable with the tuning sleeves 14a and 14h. In thiscase, *the rider 142 constitutes the rounded outer end of a member orbar 144 which is secured to the block 30. It will be seen that the,member 144 iS integral with ,the member 93,

The cam 118 is biased against the rider 142 by means of a spring 146. Inthis case, the spring 146 is stretched between the arm 128 and afixedanchor 148, so as to bias the lever 122 in a clockwise direction.

The shape of the cam 11S will determine the manner in whichthe couplingis varied as the tuning sleeves 14a and 14b are moved along the coils20. The cam plate 118 may be curved, to provide a progressive change incoupling, or generally llat, as shown, to aord relatively constantcoupling.

The illustrated cam 118 is formed with a large nurnber of spacedtransverse slots 159 which divide the cam into a large number ofindividually bendable tabs or lingers 152. As the tuning sleeves 14a and1411 are moved along the coils, the rider 142 will engage each of thetabs 152 in turn. At any particular position of the tuning sleeves 14aand 11b, the coupling may be adjusted by bending the tab 152 which isengaging the rider 142. This will change the position of the cam 118,and hence will move the coupling electrodes 116. By proper adjustment ofthe tabs 152, the coupling may be con-Y trolled so as to maintainsubstantially constant band width throughout the tuning range of thetuner 10.

FIGS. 5 and 6 illustrate a somewhat modiiied variable tracking device156. The tuning sleeve 14a and the coil 2t) of FIGS. 5 and 6 may besubstantiallythe same as in FIGS. 1-4. However, the shielding tube 24ais dispensed with in fFIGS. 5 and 6. Instead, a connection is made tothe movable sleeve 14a by means of a iiexible conductive rod 158 securedto the sleeve. It will be understood that the rod 158 may be connectedto a suitable circuit and a suitable operating mechanism.

The arrangement of FIGS. 5 and 6 may also utilize the stationaryadjustable cam plate 76 of FIGS. 1-3. As before, the plate 76 is formedwith a large number of individually bendable tabs or fingers 166, withslots 104 therebetween.

Much as in FIGS. l4, the tracking device 156 employs a movable trackingmember in the form of a ring 166 which is disposed around the coil 26 atone end of the tuning sleeve 14a. The ring 160 is mounted on the sleeve14a for generally axial movement relative thereto, so as to cause smallchanges in the tuning of the coil 2t). In the illustrated construction,a generally U-shaped spring 162 is connected between the sleeve 14a andthe ring 160. Thus, the spring 162 has a rst leg 164 which is secured tothe sleeve 14a, and a second leg 166, secured to the ring 160. A camfollower 168 is mounted on the leg 166 for engagement with the cam 76.As shown, the follower 168 simply takes the form of a rounded buttonsecured to the spring leg 166.

The spring 162 biases the follower 168 against the cam plate 76, so thatthe follower Will move laterally in conformity with any lateraldeviations of the tabs 106. Any movement of the follower 168 ,Will causethe ring 16@ to swing toward or away from the tuning sleeve 14a. Thiswill change the tuning of the coil 20 to a suflicient extent to trackthe coil with one or more similar coils. By bending the individual tabs166, the tuning of the coil 20 may be tracked to the desired tuningcurve, throughout the tuning range.

Thus, the illustrated tuners provided for adjustment of both thetracking and the coupling between two or more timed circuits. Simply bybending the tabs on the adjustable cams, the tracking and coupling maybe adjusted throughout the tuning range.

Various other modifications, alternative constructions and equivalentsmay be employed without departing from the true spirit and scope of theinvention, as exemplified in the foregoing description, and dened in thefollowing claims:

We claim:

l. In a radio frequency tuner, the combination comprising first andsecond coils, first and second tuning .sleeves movable along saidrespective coils, an operating member secured to said rst and ,secondsleeves, a lead screw in threaded engagement with said operating memberfor moving said sleeves along said coils, a tracking ring receivedaround said rst coil adjacent one end of said rst sleeve, means mountingsaid ring on said first sleeve for axial movement relative thereto, astationary comb-like cam plate extending generally parallel to the pathof movement of said first sleeve, a cam follower engaging said camplate, means connecting said follower to said tracking ring for movingsaid ring in respouse to movement of said follower, said cam platehaving a large number of closely spaced fingers thereon extendingtransversely to the direction of movement of said rst sleeve, each ofsaid fingers being individually endable for adjusting the position ofsaid tracking ring when said cam follower is engaging said nger, acoupling member extending between said first and second coils andmovable along said coils to vary the amount of coupling therebetween, arotatable shaft extending substantially parallel to the paths of saidsleeves, means connecting said shaft tcsaid coupling member for movingsaid coupling member in response to rotation of said shaft, a second camplate secured to said shaft and extending generally parallel to thepaths of said sleeves, a cam rider secured to said operating member andengaging said second cam plate, biasing means for maintaining saidsecond cam plate in engagement with said cam rider, said second camplate having a large number of closely spaced fingers thereon extendingtransversely to the length of said second cam plate and disposed forsuccessive engagement by said cam rider, each of said fingers on saidsecond cam plate being individually bendable to adjust the couplingbetween said coils when said cam rider is engaging each of such fingers.

2. in a radio frequency tuner, the combination comprising first andsecond tuning devices, each of said devices having a tuning membermovable along a predetermined path to vary the operating frequency ofsaid tuning device, an operating member connected to said tuning membersfor simultaneously moving said tuning members along said paths, said rsttuning device having a tracking member mounted on said tuning memberthereof for movement relative to such tuning member for effecting slightvariations in the operating frequency of said first tuning device, afirst cam plate extending generally parallel to the path of said tuningmember of said first tuning device, a movable cam follower engaging saidcam plate and mounted on said tuning member of said first tuning device,means connecting said cam follower to said tracking member for movingsaid tracking member in response to movement of said follower, said camplate having a plurality of individually bendable tabs spaced therealongfor adjusting the position of said cam follower when engaging each ofsaid tabs, a movable coupling element for adjusting the amount ofcoupling between said first and second tuning devices, a second camplate extending generally parallel to the path of movement of saidoperating member and movable transversely to such path, a cam riderengaging said second cam plate and secured to said operating member,means connecting said second cam plate to said coupling member formoving said coupling member in response to transverse movement of saidsecond cam plate, said second cam plate having a plurality ofindividually bendable tabs thereon spaced therealong for successiveengagement by said cam rider to adjust the coupling between said tuningdevices when said rider is engaging each of said tabs.

3. In a radio frequency tuner, the combination comprising a pair oftiming devices having respective tuning members movable alongsubstantially parallel paths for varying the operating frequencies ofsaid turning devices, an operating member connected to said tuningmembers for effecting simultaneous movement thereof, a movable couplingmember for varying the amount of coupling between said tuning devices, acam extending along the path of said operating member and movabletransversely to such path, a cam rider secured to said operating memberand engaging said cam, and means for connecting said cam to saidcoupling member for moving said coupling member in response totransverse movement Of said cam, said cam being generally comb-like inshape and having a` plurality of tabs spaced therealong and successivelyengageable by said cam rider for adjusting the position ot said couplingmember when said rider is engaging each of said tabs,

4. ln a radio frequency tuner, the combination comprising first andsecond tuning devices, each of said devices having a movable timingmember for varying the operating frequency of said tuning device, meansfor simultaneously moving said tuning members, said first tuning devicehaving a tracking member movable relative to such tuning member foreffecting slight variations in the operating frequency of said rsttuning device, a first cam extending along the path of said tuningmember of said first tuning device, a movable cam follower engaging saidcam, means connecting said cam follower to said tracking member formoving said tracking member in response to movement of said follower,said cam having a plurality of individually adjustable elements spacedtherealong for adjusting the position of said cam follower when engagingeach of said elements, a movable coupling element for adjusting theamount of coupling between said first and second tuning devices, amovable second cam extending adjacent said tuning members, a cam riderengaging said second cam and movable with said tuning members, meansconnecting said second cam to said coupling member for moving saidcoupling member in response to movement of said second cam, said secondcam `having a plurality of individually adjustable elements thereonspaced therealong for successive engagement by said cam rider to ad justthe coupling between said tuning devices when said rider is engagingeach of such adjustable elements.

5. In a radio frequency tuner, the combination comprising first andsecond coils, rst and second tuning members movable along saidrespective coils, means for moving said members simultaneously alongsaid coils, a tracking member adjacent one end of said first tuningmember, means mounting said tracking member on said first member formovement relative thereto, a stationary cam plate extending generallyparallel to the path of movement of said rst tuning member, a camfollower engaging said cam plate, means connecting said follower to saidtracking member for moving said ring in response to movement of saidfollower, said cam plate having a plurality of individually bendableportions for adjusting the position of said tracking ring when said camfollower is engaging each portion, a coupling member extending betweensaid first and second coils and movable along said coils t0 vary theamount of coupling therebetween, a rotatable shaft extendingsubstantially parallel to the paths of said timing member, meansconnecting said shaft to said coupling member for moving said couplingmember in response to rotation of said shaft, a second cam plate securedto said shaft and extending generally parallel to the paths of saidtuning members, a cam rider movable with said tuning members andengaging said second cam plate, biasing means for maintaining saidsecond cam plate in engagement with said cam rider, said second camplate having a plurality of individually bendable elements disposed forsuccessive engagement by said cam rider to adjust the coupling betweensaid coils when said cam rider is engaging each of such elements.

6. In a radio frequency tuner, the combination comprising a tuning coil,a conductive tuning sleeve received around said coil and movabletherealong for varying the resonant frequency of said tuner, meansproviding dielectric material between said sleeve and said coil, atracking ring movably mounted on said sleeve and received around saidcoil adjacent said sleeve, said tracking ring being movable relative tosaid sleeve for eiecting slight variations in the resonant frequency ofsaid tuner, a stationary cam, extending along said coil, a cam followerengaging said cam and mounted on said tuning sleeve for movementtherewith along said coil, said follower being movable relative to saidtuning sleeve by said cam, means connecting said cam follower to saidtracking ring for moving said tracking ring in response to movement ofsaid follower by said cam, said cam being generally comb-like in shapeand having a plurality of individually bendable tabs spaced therealongfor successive engagement by said cam follower to adjust the position ofsaid tracking ring when said cam follower is engaging each of said tabs.

References Cited in the tile of this patent UNITED STATES PATENTS1,577,613 Dunmore Mar. 23, 1926 2,290,705 Pfost July 21, 1942 2,468,071Hunter Apr. 26, 1949 2,505,572 Overacker Apr. 25, 1950 2,808,506 SkwarekOct. l, 1957 2,883,864 Mason Apr. 28, 1959

